1. Field of the Invention
The present invention relates generally to semiconductor manufacturing devices, and more particularly, to a semiconductor manufacturing device for baking a wafer in the process of photolithography.
2. Description of the Background Art
In the process of photolithography in the manufacture of semiconductor devices, resist is applied on a wafer and patterned into a prescribed shape. At the time, the resist is subjected to various baking processes including dehydration bake (DH), adhesion bake (AD), pre-bake (PB), post-exposure bake (PEB), and post-development bake (PDB).
FIG. 4 shows an example of a semiconductor manufacturing device, a hot plate unit 1 capable of performing the baking processes as described above. Referring to FIG. 4, hot plate unit 1 has a bake plate 3 provided in a chamber 8 and a cover 2. Bake plate 3 is continuously placed in a heated state by a heater, and held at a prescribed temperature. Cover 2 has an outlet 6 and an inner wall face 2c. Hot plate unit 1 is provided with an inlet 9 for taking in gas into chamber 8.
A method of baking using hot plate unit 1 having the above-described structure will be now described. A wafer 7 is placed on bake plate 3 in chamber 8 by a robot arm and the like. At the time, wafer 7 and bake plate 3 are brought into a close contact state or a point-contact state (proximity bake). Chamber 8 is filled with air, DA (Dry Air), N.sub.2 and the like. In the state, wafer 7 is subjected to a baking processing for a prescribed time period. During the period, the gas is constantly let out from outlet 6 provided at cover 2 at 2 to 3 L (liter)/min. After wafer 7 has been thus baked, wafer 7 is taken out from chamber 8, and the baking completes.
As described above, conventional hot plate unit 1 is devised to improve the displacement efficiency by providing outlet 6 and inclining the inner wall face 2c of cover 2. The amount of displacement is about as large as 2 to 3 L/min in order to restrict crystallization of a sublimate in chamber 8.
While such a countermeasure to sublimation is important, wafer 7 should be evenly baked as well. This is because how evenly wafer 7 has been baked affects the uniformity of line width or the like on a main surface 7a after patterning.
FIG. 5 shows a distribution of hole sizes (a distribution within a wafer surface) in the main surface 7a of wafer 7 after a hole size reducing process using a thermal flow of resist by conventional hot plate unit 1. As shown in FIG. 5, hole sizes in the central portion of wafer 7 are extremely larger than those in the other parts. This shows that wafer 7 could hardly be evenly baked by conventional hot plate unit 1. This is probably because conventional hot plate unit 1 as described above does not take much into account the effect of air flow within chamber 8 or radiant heat from cover 2. Hence, such conventional hot plate unit 1 cannot be used for a process sensitive to heat treatment, a hole size reducing process in particular.